Layer: Foundation · Build flags: PC_ENABLE_ETHERNET, ETH_PHY_*

What this example teaches

Some deployments want a wired uplink - PoE cameras, panel-mount controllers, RF-noisy factory floors, anything that can't rely on Wi-Fi. With PC_ENABLE_ETHERNET the physical layer gains init_eth_physical() alongside init_wifi_physical():

init_eth_physical();          // ETH.begin() with the ETH_PHY_* build-flag config
while (!eth_ready()) delay(250);
// ... server.begin(80) - now serving over Ethernet

It is a thin wrapper over the Arduino ETH library for an RMII PHY (LAN8720 / TLK110 / RTL8201 / DP83848). Nothing else changes: the egress reporting already classifies a wired route as PC_IFACE_ETH, so pc_net_egress(), per-route STA/AP/ETH interface filters, and every protocol work over the wired link the moment it has an IP. Wi-Fi and Ethernet can also run together (dual-homed) - the stack picks the default route.

PHY configuration

The PHY pins, address, type, and clock source come from the standard ETH_PHY_* build flags (they vary by board). This example is tuned for a generic LAN8720:

Flag	Value
`ETH_PHY_TYPE`	`ETH_PHY_LAN8720`
`ETH_PHY_ADDR`	`1`
`ETH_PHY_POWER`	`-1` (none)
`ETH_PHY_MDC`	`23`
`ETH_PHY_MDIO`	`18`
`ETH_CLK_MODE`	`ETH_CLOCK_GPIO0_IN`

Common boards differ - e.g. WT32-ETH01 uses ETH_PHY_POWER=16, Olimex ESP32-POE uses ETH_PHY_ADDR=0 ETH_PHY_POWER=12 ETH_CLK_MODE=ETH_CLOCK_GPIO17_OUT. Set the flags for your hardware.

ESP32-P4 (verified)

On the ESP32-P4 the RMII PHY drives the P4's built-in EMAC (no external SPI chip). A board whose arduino-esp32 variant already defines the ETH_PHY_* pins needs no ETH_PHY_* flags - init_eth_physical()'s no-arg ETH.begin() picks them up. HW-verified (2026-07-19) on a Waveshare ESP32-P4-POE-ETH (onboard IP101 PHY: MDC=31 MDIO=52 POWER=51, EMAC_CLK_EXT_IN, phy addr 0) built under arduino-esp32 3.x - link came up 100M full-duplex + DHCP and the server answered HTTP over pure wired Ethernet:

# arduino-esp32 3.x; the waveshare_p4_poe_eth variant supplies the IP101 pins, so only the library
# flag is needed:
arduino-cli compile --fqbn esp32:esp32:waveshare_p4_poe_eth \
  --build-property "compiler.cpp.extra_flags=-DPC_ENABLE_ETHERNET=1" \
  examples/Peripherals/Ethernet/Ethernet.ino

For a P4 board without a ready-made variant, pass the pins explicitly (from the board's schematic), e.g. -DPC_ENABLE_ETHERNET=1 -DETH_PHY_TYPE=ETH_PHY_IP101 -DETH_PHY_ADDR=0 -DETH_PHY_MDC=31 -DETH_PHY_MDIO=52 -DETH_PHY_POWER=51 -DETH_CLK_MODE=EMAC_CLK_EXT_IN.

Build-flag note

The flags must reach the library build, so pass them as build flags:

pio ci --board=esp32dev --project-option="framework=arduino" \
  --project-option="build_flags=-DPC_ENABLE_ETHERNET=1 -DETH_PHY_TYPE=ETH_PHY_LAN8720 -DETH_PHY_ADDR=1 -DETH_PHY_POWER=-1 -DETH_PHY_MDC=23 -DETH_PHY_MDIO=18 -DETH_CLK_MODE=ETH_CLOCK_GPIO0_IN" \
  --lib="." examples/Peripherals/Ethernet/Ethernet.ino